The prime objectives of this research project are to characterize leukemia specific (or associated) membrane antigens and membrane alloantigen systems, which are controlled by genes within the major histocompatibility complex, by immunochemical methods and to isolate the antigens in sufficient amounts for structural determinations and immunobiological studies. Human lymphoid cell lines are being used for this purpose since they are a very good source for obtaining these immunobiologically important cell products, since they retain a variety of biological functions which include synthesis of immunoglobulins, HL-A antigens, stimulating substances in MLC reaction, lymphokines and leukemia associated antigens and they represent uniform cell population and the supply can be relatively unlimited in amount. The very sensitive and quantitative radioimmunoassay method involving the use of radioiodinated reference antigen which has been extensively employed by us in HL-A studies has made possible our success in quantitative assay and the isolation studies of the HL-A antigens and should be just as effective in the isolation of other membrane components.